Prior art electrical vehicles typically incorporate a brushed motor gearbox train and require a substantial bank of batteries in order to operate. The use of a gearbox train to transfer the power from the motor to the four wheels causes losses in efficiency. Sometimes as much as 50% of the power input to the electric motor is lost before being transferred to the wheels of the vehicle.
Electric vehicles incorporating In-wheel electric motor systems have been developed in the past that have sought to overcome the issue of loss of power and reduced efficiencies associated with conventional electric drive trains. Whilst these in-wheel electric motor vehicles have lower power losses and are more efficient, these vehicles have associated with them, the problem of poor road holding performance. The reason these vehicles perform badly on the road is a result of increases in their so-called “un-sprung mass”.
The un-sprung mass of a ground vehicle with a suspension is the mass of the suspension, wheels or tracks (as applicable), and other components directly connected to them. The mass of the body and other components supported by the suspension is the sprung mass. Un-sprung mass includes the mass of components such as the wheel axles, wheel bearings, tyres, springs, shock absorbers, and suspension links.
As the un-sprung mass of a vehicle increases, the contact force of a tyre fluctuates when the vehicle runs over an uneven road, resulting in deteriorated road holding properties.
When in-wheel motors are utilised instead of a central electric motor the effect on the un-sprung and sprung masses are twofold. Firstly the sprung mass of the vehicle decreases as the motor and transmission which originally sat on a suspended chassis is taken off the chassis. Secondly, since the motor stator of the in-wheel motor is rotatably fixed to a spindle shaft connected to a part called an “upright” or “knuckle” which is one of the parts around the wheels of the vehicle, the un-sprung mass of the vehicle increases when an in-wheel motor is mounted, thereby deteriorating the road holding properties of the vehicle.
As a result of the large un-sprung masses associated with in-wheel electric motors, the road holding performance, and consequently safety, of these vehicles is seriously compromised.
Even when the mass of the body of a vehicle, so-called “sprung mass” is small, the road holding properties of such vehicles deteriorates when in-wheel electric motors are used. As a result, the in-wheel motor vehicle is rarely used although it is a very attractive electric car having excellent space efficiency and transmission efficiency of driving force.
One attempt at overcoming the problem of increased sprung mass when in-wheel electric motors are introduced into a vehicle to replace a centrally mounted electric motor is to be found in U.S. Pat. No. 7,306,065 which discloses a method of mounting an in-wheel motor and an in-wheel motor system both of which are capable of reducing the tyre contact force fluctuation of a vehicle to improve the road holding properties of the vehicle so as to overcome the abovementioned problems of the earlier prior art. However, the way in which the inventor has done this is to introduce very complicated and sophisticated active suspension components that constantly monitor pressures exerted on the wheels by the terrain and by the suspended chassis to compensate for the differences in pressures through the use of active suspension components. Such an approach adds complexity and raises the cost to manufacture in-wheel electric vehicles.
The problems caused by un-sprung mass result in the introduction of variable force between the wheel and the ground. This can result in wheels locking under braking or spinning even under minimal acceleration and especially under strong acceleration. This locking and spinning contributes further to the poor road-holding experienced in the general motor vehicle industry.
It has been determined by the present inventor that by reducing the mass of in-wheel electric motors and by reducing the un-sprung mass of the vehicle generally it is possible to design a vehicle that uses in-wheel electric motors without active suspension and which has acceptable road holding performance. In particular, it has been discovered that a golf course or resort vehicle with in-wheel electric motors mounted on traditional suspension components, can adequately maintain grip on the road and provide acceptable road holding performance. As will be described below, if in-wheel electric motors weighing up to 7 kg (which provide up to 1 KW in power output) are utilised in a golf course or resort vehicle of approximately 450 kg, performance will be adequate for most road conditions encountered. If however, the road and or other surface conditions are going to challenge the vehicle, for instance, unsealed road surfaces, or hilly terrain, active control systems are provided by the present invention which result in good road holding performance without the need to provide active suspension.
The inventor has found that anti-lock braking, active traction control and providing electronic differential speed controls, when provided in an electric vehicle fitted with in-wheel electric motors, overcome the previously documented problems associated with un-sprung mass without the need to provide active suspension components.
Golf course or resort vehicles are fairly small in dimension, and often lack components such as a roof, windows and doors. Typically these vehicles are generally around 4 feet (1.2 m) wide×8 feet (2.4 m) long×6 feet (1.8 m) high and weigh 900 pounds (410 kg) to 1,000 pounds (450 kg) (which is more than half the weight of highway vehicles). Such a vehicle equipped with in-wheel electric motors will end up having a maximum speed of 30 kph which is more than enough for use as a:
(a) golf course car;
(b) resort car;
(c) CBD/metro car;
(d) utility vehicle for carrying a payload such as landscaping material;
(e) factory or studio vehicle;
(f) airside airport vehicle.
Thus although the present invention will be described by reference to a “golf course and resort vehicle” the person skilled in the art will appreciate that the term applies to any vehicle of relatively small dimensions and weight and which is principally concerned with transporting people, or other payload, short distances at low speed.